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swahlgren1-Visitor
1-Visitor
Sep 22, 2014 1:59 PM UTC
Solved

Solving equations using using arrays

The attached contains an expression I wish to use in a solver to determine x-amount of constants (the Q's) from a system of an equal amount of equations and unknowns (the constants). The problem in mathcad arises when I'm using multiple (two) arrays within the solve block.

RichardJAnswer
19-Tanzanite
Sep 25, 2014 1:51 PM UTC

As already suggested, get rid of the summation and the indexing.

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13 replies

Werner_E
Werner_E25-Diamond I
25-Diamond I
Sep 22, 2014 2:08 PM UTC

You will have to specify a value for n first.

You will also have to provide at least a sample for the vector u and the square matrix lamda.Q so we have soemthing to play with.

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Werner_E
Werner_E25-Diamond I
25-Diamond I
Sep 22, 2014 2:16 PM UTC

Can it be that you are looking for something like the attached?

EDIT: Of course you can get the result much easier using the inverse:

1.png

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swahlgren1-VisitorAuthor
1-Visitor
Sep 22, 2014 2:52 PM UTC

Something like that but I need to include summation over one of the indices.

Untitled.png

"Funny" thing is I got it working a few minutes ago but the Mathcad shut down spontaneously and I can't get it working again. The error message is:"This variable is undefined"

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Werner_E
Werner_E25-Diamond I
25-Diamond I
Sep 22, 2014 3:13 PM UTC

What you set up with your sum is exactly the multiplication of the matrix lamda.Q with the vector Q - thats the reason I posted my sheet in the last message.

The error messages in solve blocks are misleading - you will always get that "undefined variable", no matter what the real cause is. Right klick at the error message and chose "Trace Error" to get at least a message which may be a bit more useful.

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